Bones, Bone Structure, and Joints: Study Guide for Anatomy & Physiology

Bones and Bone Structure

Bone Classifications

Bones are classified based on their shape and structure, which relates to their function in the body.

• Long Bones: Longer than they are wide (e.g., femur, humerus). Function in movement and support.

• Short Bones: Nearly equal in length and width (e.g., carpals, tarsals). Provide stability and some movement.

• Flat Bones: Thin, flattened, and often curved (e.g., sternum, ribs, skull bones). Protect internal organs and provide surfaces for muscle attachment.

• Irregular Bones: Complex shapes (e.g., vertebrae, pelvic bones).

• Sesamoid Bones: Small, round bones embedded in tendons (e.g., patella).

Compact vs. Spongy Bone

Bones contain two main types of osseous tissue:

• Compact Bone: Dense and solid, forms the outer layer of bones. Contains osteons (Haversian systems), which are cylindrical structures that provide strength.

• Spongy Bone: Also called cancellous bone, found at the ends of long bones and inside flat bones. Contains a network of trabeculae (thin columns), which help resist stress and house bone marrow.

Articular Cartilage

• Location: Covers the ends of bones at synovial joints.

• Function: Reduces friction and absorbs shock during movement.

• Type: Made of hyaline cartilage.

Hormonal Regulation of Bone Growth

• Calcitonin: Lowers blood calcium by inhibiting osteoclast activity and stimulating calcium deposition in bones.

• Parathyroid Hormone (PTH): Increases blood calcium by stimulating osteoclasts to break down bone matrix.

• Growth Hormone, Sex Hormones, and Thyroid Hormones: Also influence bone growth and remodeling.

Appositional Bone Growth

• Bone increases in diameter as new bone tissue is added to the surface by osteoblasts in the periosteum.

Ossification: Intramembranous vs. Endochondral

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue. Forms flat bones like the skull and clavicle.

• Endochondral Ossification: Bone replaces a cartilage model. Forms most bones, including long bones.

Bone Cells: Osteoblasts vs. Osteoclasts

• Osteoblasts: Build new bone matrix (bone formation).

• Osteoclasts: Break down bone matrix (bone resorption).

Disorders of Bone Growth

• Pituitary Dwarfism: Insufficient growth hormone; results in short stature with normal proportions.

• Gigantism: Excess growth hormone before epiphyseal plates close; abnormally tall stature.

• Acromegaly: Excess growth hormone after epiphyseal plates close; enlarged hands, feet, and facial features.

Structure of a Long Bone

• Diaphysis: Shaft; provides leverage and weight support.

• Epiphyses: Ends; contain spongy bone and red marrow.

• Metaphysis: Region between diaphysis and epiphysis; contains growth plate.

• Medullary Cavity: Central cavity containing marrow.

• Periosteum: Outer covering; contains nerves and blood vessels.

• Endosteum: Lines the medullary cavity.

Bone Marrow: Red vs. Yellow

• Red Marrow: Site of blood cell production (hematopoiesis); found in children and in adult flat bones.

• Yellow Marrow: Stores fat; increases with age as red marrow is replaced.

Hydroxyapatite

• Definition: Crystalline mineral compound of calcium and phosphate ($Ca_{10}(PO_4)_6(OH)_2$).

• Importance: Provides hardness and strength to bone matrix.

Functional Unit of Bone

• Osteon (Haversian System): The structural and functional unit of compact bone.

The Skeleton

Bone Identification and Structures

• Be able to identify major bones and their anatomical features (e.g., femur, humerus, vertebrae, skull bones).

Skull Sutures

• Sutures: Immovable joints between skull bones (e.g., coronal, sagittal, lambdoid, squamous).

Sinuses

• Function: Lighten the skull, produce mucus, and enhance voice resonance.

Fontanels

• Definition: Soft spots on infant skulls where bone formation is incomplete.

• Function: Allow for brain growth and passage through the birth canal.

Vertebral Issues

• Osteoporosis: Decreased bone mass and increased fracture risk.

• Osteopenia: Mild reduction in bone mass, precursor to osteoporosis.

• Other Issues: Scoliosis, kyphosis, lordosis (abnormal spinal curvatures).

Rib Articulations

• Ribs articulate with thoracic vertebrae and the sternum (via costal cartilage).

Pelvic Bones

• Ischial Tuberosity: The part of the pelvis you sit on.

Male vs. Female Skeleton

• Pelvis: Female pelvis is wider and shallower for childbirth.

• Skull: Male skulls are generally larger and more robust.

Joints

Types and Classification of Joints

• Fibrous Joints: Immovable (e.g., sutures of the skull).

• Cartilaginous Joints: Slightly movable (e.g., intervertebral discs).

• Synovial Joints: Freely movable; most common type (e.g., knee, shoulder).

Synovial Joint Structure

• Articular Cartilage: Covers bone ends.

• Joint (Synovial) Cavity: Space filled with synovial fluid.

• Articular Capsule: Encloses the joint cavity.

• Synovial Fluid: Lubricates and nourishes cartilage.

• Ligaments: Strengthen and support the joint.

Knee Joint

• Largest and most complex synovial joint; includes menisci, cruciate ligaments, and collateral ligaments.

Joint Movements

• Adduction: Movement toward the midline.

• Abduction: Movement away from the midline.

• Other Movements: Flexion, extension, rotation, circumduction, etc.

Arthritis Types

• Osteoarthritis: Degenerative joint disease; cartilage wears down.

• Rheumatoid Arthritis: Autoimmune inflammation of joints.

• Gouty Arthritis: Uric acid crystal accumulation in joints.

Calcium Homeostasis

Systems Maintaining Blood Calcium

• Skeletal System: Stores and releases calcium.

• Digestive System: Absorbs calcium from food.

• Urinary System: Excretes or conserves calcium.

Summary Table: Bone Cells and Functions

Cell Type	Function
Osteoblast	Builds bone matrix
Osteoclast	Breaks down bone matrix
Osteocyte	Maintains bone tissue

Summary Table: Types of Joints

Joint Type	Movement	Example
Fibrous	Immovable	Sutures of skull
Cartilaginous	Slightly movable	Intervertebral discs
Synovial	Freely movable	Knee, shoulder

Example: Bone Growth Regulation

• When blood calcium drops, PTH is released, stimulating osteoclasts to break down bone and release calcium into the blood.

• When blood calcium is high, calcitonin is released, inhibiting osteoclasts and promoting calcium deposition in bone.

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard Anatomy & Physiology content.